1. Field of the Invention
This invention relates generally to internal combustion reciprocating engines, and more particularly to the delivery of the combustion air to the cylinders.
2. Description of the Prior Art
There are continuous efforts in the engine industry to improve performance while reducing size, weight and cost of engines. One technique with diesel engines has been to use two intake valves and two exhaust valves for each cylinder. In some cases, air is supplied to the cylinders through only one intake valve port for low load operation, and through both intake valve ports for high load operating conditions. For example, U.S. Pat. No. 5,094,210 to Endres et al., discloses an intake and fuel/air mixing system for multi-cylinder, externally ignited internal combustion engines with at least two valves per cylinder and at least two separate intake pipe arms per cylinder. One of the two intake pipe arms for each cylinder is supplied from one air inlet common to the first group of intake pipe arms. The other of the two pipe arms for each cylinder is supplied from another air inlet common to the second group. The patent discloses a method for controlling the air flow rate to the cylinders by means of throttling members such that the first group opens first by means of throttling member I-7 for engine operating regions of low flow rates, with the other group being opened by operating throttling member II-10 as a function of the speed and load for higher flow rates.
For valve-in-head engines, cross-flow cylinder heads (where the intake ports are located on one side of the cylinder head and the exhaust ports on the other) are the optimum arrangement from a gas transport standpoint. An example of a cross-flow head is shown in U.S. Pat. No. 5,007,392 to Niizato et al. (FIG. 2). But cross-flow heads are difficult to design for a pushrod engine, because pushrods and intake ports have conflicting space requirements.
The results of some design studies for cross-flow heads for pushrod engines are described in a publication by The Society of Automotive Engineers (SAE) in a technical paper No. 900133 written by Nigel F. Gale of the Southwest Research Institute entitled Diesel Engine Cylinder-Head Design: The Compromises and Techniques. FIGS. 22 and 23 in that paper show cross-flow four-valve cylinder head layouts. The FIG. 23 version shows a layout using an intake runner which is shared by the helical intake port of one cylinder and a tangential "directed" intake port of an adjacent cylinder where the ports are arranged in a "diamond" configuration. This is described on page 12 of the paper. I think the configuration shown and described in that publication would result in undesirable flow characteristics. Therefore, an object of the present invention is to provide an improved cross-flow, four-valve cylinder head useful with pushrod operated or overhead cam engines and laving improved intake gas flow characteristics.